Change Video Aspect Ratio
Change a video’s aspect ratio with contain when every edge must remain visible, or cover when the target frame must be full. Contain keeps the complete picture and leaves blank space. Cover fills the frame and crops the overflow. For the same source and target ratios, the blank-space percentage and crop percentage are equal. Never stretch the picture to force a fit.
Choose the target aspect ratio before changing the video
Write the source ratio as Rs = Ws / Hs and the target ratio as Rt = Wt / Ht. The frame cost depends on those two ratios, not on the editing application.
How do I calculate the cost of changing video aspect ratio?
Occupied share = min(Rs, Rt) / max(Rs, Rt)
Blank or cropped share = 1 - occupied share
The percentage is the same for both methods. Contain pays that percentage as blank frame area along one dimension. Cover pays it as cropped picture along the opposite dimension.
Contain: preserve the whole video
If the source is wider than the target, fit by width and leave space above and below. If the source is narrower than the target, fit by height and leave space on the left and right.
Cover: fill the target frame
If the source is wider than the target, fill by height and crop the left and right edges. If the source is narrower than the target, fill by width and crop the top and bottom edges.
Contain and cover pay the same percentage. Contain gives up frame space; cover gives up picture content.
Video aspect ratio conversion cost table
| Source and target | Contain blank share | Cover crop share | Share on each centered side |
|---|---|---|---|
| 16:9 ↔ 9:16 | 68.36% | 68.36% | 34.18% |
| 16:9 ↔ 4:3 | 25.00% | 25.00% | 12.50% |
| 16:9 ↔ 1:1 | 43.75% | 43.75% | 21.875% |
| 4:3 ↔ 1:1 | 25.00% | 25.00% | 12.50% |
| 9:16 ↔ 1:1 | 43.75% | 43.75% | 21.875% |
| 16:9 ↔ 21:9 | 23.81% | 23.81% | 11.905% |
| 9:16 ↔ 4:3 | 57.81% | 57.81% | 28.905% |
The displayed percentages are rounded from the exact ratio calculation. The same value applies in either direction because swapping source and target does not change min(Rs, Rt) / max(Rs, Rt).
How do I contain a 16:9 video inside a 9:16 frame?
This example uses a 1648 × 927 source and a 927 × 1648 target so the dimensions do not repeat another worked example on this site.
- 1Fit the source to the target width
The scale is 927 / 1648 = 0.5625.
- 2Calculate the contained height
927 × 9 / 16 = 521.4375 pixels.
- 3Split the remaining target height
1648 - 521.4375 = 1126.5625 pixels. Centering leaves 563.28125 pixels above and below.
The combined blank share is 1126.5625 / 1648 = 68.359375%, displayed as 68.36%. Each centered bar is 34.1796875% of the target height, displayed as 34.18%.
Cover has the same 68.36% cost. Filling the target height scales the source width to 1648 × 16 / 9 = 2929.7778 pixels. A centered crop removes 2002.7778 pixels in total, or 1001.3889 pixels from each side.
Do not stretch a video to match another aspect ratio
Stretching is not a valid fit method. It fills the frame by scaling width and height by different factors, which makes people and objects look compressed or widened. Use contain, cover, or redesign the composition for the target frame. If a video already looks stretched, the cause is usually the sample-aspect or display-aspect metadata rather than the pixels: diagnose a stretched video before re-encoding it.
Change video aspect ratio questions
Can I change video aspect ratio without cropping?
Yes. Use contain. It keeps the full picture and places any unused space around it as bars.
How do I fill a new aspect ratio without black bars?
Use cover. Scale until the target frame is full, then crop the picture that extends beyond the target edges.
Why do contain and cover have the same percentage cost?
Both compare the same two ratios with min(Rs, Rt) / max(Rs, Rt). Contain expresses the remainder as blank frame space, while cover expresses it as cropped source content.
Should I stretch a video to fit the target frame?
No. Stretching changes geometry. Contain preserves the full picture, and cover preserves the target frame without distorting the picture.
Sources
The ratio-pair percentages and worked pixel dimensions on this page were calculated from the formulas printed beside them and independently checked before publication. The contain and cover terms follow the behavior defined for CSS object-fit on MDN. Use the site’s aspect ratio calculator to reproduce missing-side dimensions.